Different things will happen depending on the result of your equation. Your birth month and day: Princess appears + few fireworks 123,456,789: Princess appears + many fireworks All digits the same: Coins pop out of the digits + 1UP sound plays 99,999,999: Mario jumps nine times + 1UP sound plays.
Special celebration
If you input "567+" then press "=", the level complete song will start, as well as Toad and three fireworks.